The present invention is generally directed to improving the flushability of a tissue product by the addition of a temporary wet strength agent and a bond degrading agent. More particularly, the present invention is directed to tissue products with improved flushability wherein a temporary wet strength agent is added to the tissue products in the wet end and an alkaline reagent is incorporated into the tissue products in the dry end.
Sanitary tissue products often comprise temporary wet strength agents to enhance product performance. Improved wet strength attributes are achieved as a result of the formation of covalent bonds between the cellulosic fibers of the tissue product and the wet strength agent. Such covalent bonding is typically achieved through the formation of acetal linkages between a polymeric agent such as glyoxylated polyacrylamide and the cellulosic fibers.
However, it is essential that such covalent wet strength bonds be transient in nature for sanitary bath tissue. If the covalent bonds are transient in nature, the tissue products break up more easily in water and hence exhibit improved flushability. Such tissue products with improved flushability are less injurious to septic systems.
Specifically, acetal bond formation is reversible, thus making glyoxylated polyacrylamide a good temporary wet strength agent. The covalent bonds formed are transient in nature, and thus tissue products with glyoxylated polyacrylamide incorporated therein exhibit increased flushability.
It is difficult to design a tissue product having both the desired level of wet strength to facilitate high tissue performance and the desired levels of flushability and degradability. The factors to be weighed in designing such a product include initial wet tensile strength, the rate of wet tensile loss, and the final wet tensile strength. The optimal tissue product has a high initial wet tensile strength which degrades rapidly in water to a low final wet tensile strength to aid in flushability.
A prior art tissue product made by the assignee of the present invention is known wherein baking soda has been incorporated to improve the tissue""s water break up. However, the temporary wet strength agent used for this tissue product was not glyoxylated polyacrylamide. Glyoxylated polyacrylamide specifically causes the formation of hemi-acetyl bonds that degrade much faster in a basic medium.
Thus, a need currently exists for a tissue product having high initial wet tensile strength which degrades rapidly in water to a low final wet tensile strength for improved flushability. More specifically, a need exists for a tissue product wherein an alkaline reagent has been added to the tissue product in the dry end after a temporary wet strength agent like glyoxylated polyacrylamide has been added in the wet end.
It is an object of the present invention to provide tissue products with improved flushability wherein a temporary wet strength agent has been added to the tissue product in the wet end and an alkaline reagent has been added to the tissue in the dry end.
It is another object of the present invention to add an alkaline reagent to a tissue product in a manner so that the rate of degradation is enhanced while the initial wet tensile strength of the tissue is not negatively affected.
The above objects and, perhaps, other objects are accomplished by incorporating a temporary wet strength agent such as glyoxylated polyacrylamide into a tissue product during the wet end of the tissue manufacturing process. Subsequently, the addition of an alkaline reagent in the dry end increases the pH of the tissue product and thus leads to improved degradation of the acetal bonds between the temporary wet strength agent and the cellulosic fibers of the tissue product. In certain embodiments, the amount of the alkaline reagent added may be from about 0.1 to about 5% based on the weight of the dry web of the tissue product.